Don’t Grow Your Onions Without These Companion Plants Argues Dan Ori

brown onions with green stems growing in soil in the ground outside next to each other

VEGETABLES > ONIONS > COMPANIONS

By MOLLIE BROWN / Updated September 20th, 2024
Reviewed By DAN ORI / Meets Our Editorial Guidelines
Contributions From ANN-MARIE POWELL , GERALD STRATFORD

Onions are a popular culinary delight and when grown in your garden, you’ll have the benefit of being able to harvest them whenever you like throughout the summer and autumn months.

Onions have a strong aroma, and this means that they can be a great companion plant for many different crops and other plants in your garden.

They are said to repel or confuse a range of different types of pests.

“Before you get overly excited about the potential benefits of companion planting, it is important to highlight that most companion plants benefits or efficacy have not been subject to much or any peer review studies, so we can’t say with absolute certainty that this plant benefits that plant,” says Dan Ori, Master Horticulturist.

“However, we can say that in this article the companion plants and benefits listed are most likely to be correct based on observations and applied theory.”

Onions can be usefully placed:

In mixed pots and planters.
In annual vegetable beds over winter with other overwintering crops.
Intermixed with other annual crops in kitchen garden beds in summer.
In rows intercropped between another main crop.
Around the edges of growing areas as a partial pest barrier.

Perennial types in particular can also be very useful in fruit tree guilds, forest gardens and other perennial planting schemes.

strawberries and onions being grown together in a companion planting scheme

Ideally, annual onions should be part of a crop rotation scheme, so that they are not grown in the same areas over multiple years.

So this should be considered along with companion planting when creating your planting plans.

Due to crop rotation needs, it can be useful to think about growing onions alongside other alliums (such as garlic and leeks, for example).

beetroot, onions and carrot plants growing together in a vegetable garden

However, it is important to remember that pests and diseases can pass between them, so it is generally not a good idea to grow only alliums in a particular bed or growing area.

In this guide, we share 25 different plants that make good companions for onions, from herbs to flowers to other vegetables – there is definitely an option for everyone.

1) Tomato

onions, tomatoes and beetroots growing in a raised vegetable bed inside a greenhouse

BOTANICAL NAME: Solanum lycopersicum
HARDINESS RATING: H1C
PLANT TYPE: fruit
FOLIAGE TYPE: deciduous
FLOWERS: yellow
FLOWERING SEASON(S): spring / summer
FRUIT SEASON(S): summer

Tomatoes are a great way to kick off this list.

This deciduous fruit is one of the most popular kitchen staples here in the UK and is used in a range of different recipes and dishes.

It is also frequently grown in gardens thanks to how easy they are to plant and care for once established.

Not only are tomatoes a delight in their own right, but they are also great for planting next to onions, as the smell of your alliums can deter pests that might otherwise help themselves to your tomato plants, such as whitefly and moths.

2) Spearmint

onions, mint, basil and other herbs growing in pots on a windowsill

BOTANICAL NAME: mentha spicata
HARDINESS RATING: H7
PLANT TYPE: herb / perennial
FOLIAGE TYPE: deciduous
FLOWERS: purple
FLOWERING SEASON(S): summer

Although mint has a reputation for not always being the best companion plant, it grows well with onions, as its scent can help repel onion flies and aphids that are sometimes attracted to different varieties of allium.

Also, this full hardy herb produces small purple flowers in the summer that are great for attracting pollinators and other beneficial insects.

Just be aware that spearmint can sometimes be considered invasive due to its spreading habit that can reach up to 1.5m wide, but this should not be an issue for your onions once they are established in your vegetable patch.

You can always grow your mint in pots nearby if you’re worried about them spreading.

3) Common Marigold

flowering onion growing next to some orange flowering common marigolds

BOTANICAL NAME: calendula officinalis
HARDINESS RATING: H5
PLANT TYPE: annual / biennial
FOLIAGE TYPE: deciduous
FLOWERS: orange
FLOWERING SEASON(S): summer / autumn

The first flower on this list, common marigolds are hardy annuals that bear stunning orange daisy-like flowers from May until October that will look great next to the fuzzy heads of your onion crops.

Like spearmint, marigolds are great for pollinators and will help draw beneficial insects towards your alliums if planted close together.

Marigolds are also loved by slugs, which you might think is a bad thing, but in reality, these slimy creatures will be too busy munching on their leaves to even notice your alliums.

4) Common Lettuce

purple and green lettuce growing next to a row of onions in a vegetable patch

BOTANICAL NAME: lactuca sativa
HARDINESS RATING: H2
PLANT TYPE: vegetable
FOLIAGE TYPE: deciduous
FLOWERS: yellow
FLOWERING SEASON(S): summer

Onions don’t take up much room in a vegetable patch, which is one of the reasons why they are so popular with UK home growers.

If space is a key factor in your decision-making, lettuce might just be the ideal choice for you.

Like allium, lettuce takes up most of its space underground, meaning it can be planted close to other root crops to utilise space and make more room for other plants you might wish to grow.

This vegetable is relatively easy to grow, just make sure it receives plenty of sunshine throughout the day, as lettuce thrives in sun.

5) Parsley

rows of onions and parsley growing in a field

BOTANICAL NAME: petroselinum crispum
HARDINESS RATING: H6
PLANT TYPE: biennial / herb
FOLIAGE TYPE: semi-evergreen
FLOWERS: green and yellow
FLOWERING SEASON(S): summer

Onion flies are notorious pests that feast on alliums such as onions and garlic and can cause severe damage to these crops.¹

Luckily, parsley is a fragrant herb that, if planted next to your onions, can deter these flies and keep them away from your vegetable patches.

Parsley is a small biennial that grows well in most conditions and will also provide you with aromatic foliage that can be harvested and used in your kitchen.

6) Bell Pepper

bell pepper plants in pots ready to be planted out with sprouting onion bulbs and dill

BOTANICAL NAME: capsicum annuum
HARDINESS RATING: H1C
PLANT TYPE: fruit
FOLIAGE TYPE: deciduous
FLOWERS: white
FLOWERING SEASON(S): summer
FRUIT SEASON(S): summer / early autumn

Aphids are another pesky pest that can feed on your crops and the bell pepper is one of its favourites.

As mentioned previously, onions are good at deterring some insects like aphids, so can be planted around your bell peppers to act as a barrier of protection.

This frost-tender fruit produces delicious yields and can grow well in similar conditions to onions, making it suitable for companion planting.

Be wary that this plant will struggle to survive once colder temperatures start to move in over autumn.

7) Rose ‘Yellow Meilove’

yellow flowering rose shrub growing in front of a hedge with purple flowering alliums

BOTANICAL NAME: rosa ‘yellow meilove’
HARDINESS RATING: H7
PLANT TYPE: shrub
FOLIAGE TYPE: deciduous
FLOWERS: yellow
FLOWERING SEASON(S): summer / autumn

You won’t find a garden flower that loves being planted next to onions as much as the garden rose.

As well as deterring pests that can often affect the flowers of a rose plant, onions are also said to improve the aroma of their beautiful blooms and have been planted next to roses for this reason for years.²

I’ve highlighted one of my favourite varieties ‘yellow meilove’ here, but there are lots of unfussy, fully hardy roses for you to choose from that will grow well with onions.

8) Alpine Strawberry

small strawberry plants growing in rows with a row of onions growing between them

BOTANICAL NAME: fragaria vesca
HARDINESS RATING: H6
PLANT TYPE: perennial / fruit
FOLIAGE TYPE: semi-evergreen
FLOWERS: white
FLOWERING SEASON(S): spring
FRUIT SEASON(S): summer

Strawberries are another popular fruit to grow with your onions, as they both thrive in the same conditions and will grow well together in a sheltered position in full sun.

In fact, strawberry plants can help provide some shade for your onion’s roots, which like to be kept cool, and in return, your onions can deter fruit-loving pests from going near your berries.

Alpine strawberries are a smaller variety and are great for cultivating in pots with some onions if you wish.

9) Borage

a huge sea of blue flowering borage growing next to rows of onions and beetroot

BOTANICAL NAME: borago officinalis
HARDINESS RATING: H5
PLANT TYPE: annual
FOLIAGE TYPE: deciduous
FLOWERS: blue
FLOWERING SEASON(S): summer / autumn

A hardy plant that will keep onion flies away from your onions, borage is a wonderful companion plant for alliums.

Its blue flowers that grow in clusters on long stems in the summer and autumn months look great amongst the tall, fluffy heads of onion plants and will both create a great display throughout the warmer months of the year.

Borage is also a great plant to grow in your garden regardless of its ornamental benefits, as you can use the leaves to make organic fertilisers that can assist in your vegetable’s growth when applied.

10) Garden Nasturtium

yellow and red flowering nasturtium shrub with stems of onions and dill growing between the flowers and foliage

BOTANICAL NAME: tropaeolum majus
HARDINESS RATING: H3
PLANT TYPE: climber / annual / shrub
FOLIAGE TYPE: deciduous
FLOWERS: yellow, red and orange
FLOWERING SEASON(S): summer / autumn

Nasturtiums are a great companion plant for many vegetables as they are brilliant at attracting aphids and other potential pests – keeping them from your prized crops.

They can also be used as a trap plant in a vegetable patch, encouraging slugs and snails to munch on their foliage rather than that of your onions and other crops.

A frost-tender annual, this shrub is easy to grow and will flower throughout the summer and autumn, providing some fiery colour wherever it is planted.

11) Dill

rows of onion and dill plants growing side by side in a huge vegetable field

BOTANICAL NAME: anethum graveolens
HARDINESS RATING: H4
PLANT TYPE: annual / herb
FOLIAGE TYPE: deciduous
FLOWERS: yellow
FLOWERING SEASON(S): summer

Anethum graveolens, more commonly known as dill, is an annual herb that enjoys the benefits that being planted next to onions can bring, as it can attract aphids and other bugs which onions are great at getting rid of.

However, dill can also help onions in return by means of pest control, as they are particularly good at fighting off red spider mites which can often plague alliums growing in the garden.

Dill is also a wonderful herb, most often used in Mediterranean dishes, and can be harvested in spring and summertime for use in your kitchen.³

“Dill is a really nice plant,” says Garden Designer Ann-Marie Powell.

“I love plants that grow so quickly you can almost see them growing in front of your eyes.

“They sort of explode into these starry flowers that get caught in the wind so you can see them move as well.”

12) Carrot

three rows of carrots with frilly leaves sprouting from the ground growing in between rows of onions with long, thin leaves

BOTANICAL NAME: daucus carota subsp. sativus
HARDINESS RATING: H7
PLANT TYPE: vegetable
FOLIAGE TYPE: deciduous

One of my favourite vegetables to grow each year, carrots are fully hardy vegetables that are easy to cultivate, fun to harvest and a delight when eaten raw or cooked.

Onions and carrots are a particularly effective combination, since the onions will not only help the carrots (by repelling or confusing carrot fly) – the carrots are also said to keep onion flies away.

If planting together, just make sure both plants have enough space to grow underground freely so they can reach a desirable size.

13) Bacon Weed

a chenopodium album plant with clusters of white flowers growing in a field of sprouting onion

BOTANICAL NAME: chenopodium album
HARDINESS RATING: H7
PLANT TYPE: annual
FOLIAGE TYPE: deciduous
FLOWERS: green
FLOWERING SEASON(S): summer / autumn

You might be wondering why I’ve selected a weed as one of my picks on this list, but hear me out.

Although I wouldn’t recommend planting bacon weed from seed, as it is a prolific self-seeder as it is, if this weed is growing in your vegetable patch near your onions, there is no need to panic.

In fact, bacon weed, also known as common goosefoot, can actually help to enrich the soil where alliums grow – provided its spread is kept under control.

Bacon weed can even be harvested and eaten and is often used as a substitute for lettuce for those who don’t want to waste this weed.

So next time you spot this weed growing near your onions, maybe think twice before getting rid of it completely.

14) Melon ‘Emir’

a green melon 'emir' plant with large leaves and a round, big fruit growing in a raised bed

BOTANICAL NAME: cucumis melo ’emir’
HARDINESS RATING: H1C
PLANT TYPE: fruit / annual
FOLIAGE TYPE: deciduous
FRUIT SEASON(S): summer

Melons are fruit-bearing annuals that adore onions for their fragrant aroma that helps to deter pests from their fruits.

For the purpose of this list, I’ve chosen the cultivar ’emir’, which is a tasty cantaloupe cultivar that is actually best grown under some cover, like a cloche, polytunnel or in a heated greenhouse.

They grow best in as much sunshine as possible, and onions are great for planting by their side as they are unlikely to get in the way of the warm rays this fruit needs to grow.

15) Spinach

spinach, lettuce and onions growing as companion plants in a vegetable patch

BOTANICAL NAME: spinacia oleracea
HARDINESS RATING: H4
PLANT TYPE: vegetable
FOLIAGE TYPE: deciduous

As we have established, onions are a popular companion plant because their strong scent can help to fend off pests that might pose a problem for other fruit and vegetables – spinach being another of the plants that benefit.

However, alliums are also great at bringing pollinators like ladybirds to your garden – beneficial garden predators that might feast on any pests that manage to work their way into your crops.

Spinach is often plagued by pests, so planting onions, which also thrive in the same growing conditions as this leafy vegetable, is a great way to naturally repel any harmful bugs.

16) Summer Savory

summer savory plant with tall pale stems and thin green leaves

BOTANICAL NAME: satureja hortensis
HARDINESS RATING: H4
PLANT TYPE: annual / herb
FOLIAGE TYPE: deciduous
FLOWERS: white
FLOWERING SEASON(S): summer

Planting summer savory near your onions is said to improve the taste of your crop by making them sweeter, so, if the taste is your priority, why not try planting this herb?⁴

Grown as an annual, summer savoury has its own culinary uses and is a popular substitute for salt and pepper or for use in a marinade or meat rub.⁵

This small herb needs a site in full sun but is otherwise unfussy and also produces dainty white flowers during the summer that will add some colour to your vegetable beds.

17) Kale

frilly kale plants growing with lettuce and onion plants in sunlit conditions

BOTANICAL NAME: brassica oleracea
HARDINESS RATING: H7
PLANT TYPE: vegetable
FOLIAGE TYPE: evergreen
FLOWERS: yellow
FLOWERING SEASON(S): summer / autumn

Kale is a versatile vegetable and can be used in smoothies, salads and other culinary dishes – its luscious leaves can be harvested all year round.⁶

However, as a brassica, it is vulnerable to many pests such as caterpillars and aphids, which is why kale can benefit from the pungent scent of onions that can repel these hungry bugs.

Just be aware that this vegetable prefers alkaline to neutral soil pH and will not grow well in anything acidic.

18) African Marigold

African marigolds companion planted alongside tall leafy shoots from onion plants

BOTANICAL NAME: tagetes erecta
HARDINESS RATING: H2
PLANT TYPE: annual
FOLIAGE TYPE: deciduous
FLOWERS: yellow, white and orange
FLOWERING SEASON(S): summer / autumn

One of the best plants for attracting pollinators, the African marigold can also bring beneficial insects like ladybirds to your nearby plants that will feast on any potential pests.

African marigolds bear frilly flowers throughout the summer and autumn months, will look great amongst your onions and add a touch of fiery colour to your garden plot.

These plants are easy to grow and only spread to about 50cm wide so they won’t take up too much room – leaving you with plenty of space to grow more vegetables!

19) Common Beetroot

beetroot plants with red stems and green leaves growing between onion plants in a raised garden bed

BOTANICAL NAME: beta vulgaris
HARDINESS RATING: H3
PLANT TYPE: annual / vegetable
FOLIAGE TYPE: deciduous

Beetroots love the pest-repelling odour that nearby onions can provide and are another easy-to-grow vegetable that thrives in similar conditions as others already mentioned on this list.

I love growing beetroots as part of my vegetable garden, as they grow quite quickly and their foliage also looks great, adding some leafy goodness to my plot.

20) Common Sowthistle

green sowthistle plant with a single yellow flower growing outdoors

BOTANICAL NAME: sonchus oleraceus
HARDINESS RATING: H7
PLANT TYPE: biennial
FOLIAGE TYPE: deciduous
FLOWERS: yellow
FLOWERING SEASON(S): summer

Another weed, I know, but sow thistle is actually really useful to have growing in your vegetable patches near your onions for a couple of reasons – and will not usually become too much of a nuisance.

Not only does it add nutrients to the soil it grows in like bacon weed, but this edible weed can also be harvested and used as a natural mulch, or, as it is commonly referred: ‘chopped and dropped’ onto the ground around your plants.

So, before getting rid of these weeds entirely, consider how they could benefit your onions, whether that’s in the ground or as chopped-up mulch.

21) Chamomile

chamomile plants with daisy-like flowers growing next to wild onions with purple flowers in a field

BOTANICAL NAME: chamaemelum nobile
HARDINESS RATING: H7
PLANT TYPE: herb / perennial
FOLIAGE TYPE: deciduous
FLOWERS: yellow and white
FLOWERING SEASON(S): summer

With daisy-like flowers and a small, compact size reaching no more than 50cm in height and spread, you might be shocked to learn that this little herb can actually do a lot for your onions and other vegetables.

Chamomile’s anti-fungal properties help to prevent lots of vegetables from developing fungal issues such as root rot, rust and mildew, so keeping your onions close to this perennial herb is definitely a good idea.⁷

It’s also great at repelling some common pests, so planting onions and chamomile around other vegetables in this list can really help protect them from aphids, flies and mealybugs alike.

22) Potato

potato crops growing in rows being watered with a sprinkler system and onions growing in the foreground

BOTANICAL NAME: solanum tuberosum
HARDINESS RATING: H2
PLANT TYPE: vegetable
FOLIAGE TYPE: deciduous
FLOWERS: purple and white
FLOWERING SEASON(S): spring / summer

Potatoes are a kitchen staple and make a great addition to any home grower’s garden.

Growing them next to onions is a great way to produce as big a yield as possible, as alliums don’t take up much space and won’t harm your potatoes in any way.

However, they do not like too much sun, so make sure they are placed in a shaded location or near tall crops that will protect them from the sun’s rays.

“Onions and potatoes are quite hungry plants, so you don’t want too much competition with those two,” warns Gerald Stratford, Vegetable Expert.

23) Mountain Chrysanthemum

mountain chrysanthemum with white, daisy-like flowers growing in a field with wild onions that have purple flowers

BOTANICAL NAME: leucanthemum graminifolium
HARDINESS RATING: H6
PLANT TYPE: perennial
FOLIAGE TYPE: deciduous
FLOWERS: white
FLOWERING SEASON(S): summer

The final flower to appear on this list, the mountain chrysanthemum is a daisy-like variety that benefits from onion’s ability to deter aphids with its scent.

All chrysanthemums are great pollinators and will reward your onion crops with lots of bees and butterflies that should speed up pollination and help the wildlife in your garden thrive.

24) Parsnip

large parsnips covered in soil that have been dug up with a garden fork

BOTANICAL NAME: pastinaca sativa
HARDINESS RATING: H5
PLANT TYPE: vegetables
FOLIAGE TYPE: deciduous

A delicious vegetable that will pair nicely with your onions when growing in the ground and in the kitchen, parsnips are hardy plants that grow best in similar conditions to onions and the other veggies on this list.

Like carrots, parsnips can often be damaged by carrot flies, so planting them near onions will help to keep them protected from these pests.

Parsnips prefer acidic to neutral soil, so make sure the spot you choose to grow them in is not alkaline and you will be rewarded with yummy yields.

25) Ornamental Cabbage

cabbages with big leafy foliage companion planted with wilting onion plants

BOTANICAL NAME: brassica oleracea
HARDINESS RATING: H7
PLANT TYPE: perennial / vegetable
FOLIAGE TYPE: evergreen
FLOWERS: yellow
FLOWERING SEASON(S): summer / autumn
FRUIT SEASON(S): autumn

Most brassicas come from ornamental cabbage, so this delicious vegetable is definitely one you should consider for your vegetable garden.

Unfortunately, like the other brassicas on this list, this plant is susceptible to pest damage and will enjoy the luxury of being planted next to pungent onions that will help to deter them.

Cabbage is a low-maintenance veggie and will be easy to care for once established.

References

1
Onion Maggot. (2016, October). Center for Agriculture, Food, and the Environment. Retrieved March 21, 2023, from https://ag.umass.edu/vegetable/fact-sheets/onion-maggot
2
Garlic Guide. (n.d.). An Herb Society of America Guide. Retrieved March 21, 2023, from https://www.herbsociety.org/file_download/inline/f751abad-cc5c-414f-89a5-b9e6b012ea70
3
Cornish, R. (2022, September 20). Dill: Everything you need to know. Good Food. Retrieved March 21, 2023, from https://www.smh.com.au/goodfood/everything-you-wanted-to-know-about-dill-20220908-h268tf.html
4
Tirrell, R. (1971, March 7). Summer Savory. The New York Times. Retrieved March 21, 2023, from https://Cornish, R. (2022, September 20). Dill: Everything you need to know. Good Food. Retrieved March 21, 2023, from https://www.smh.com.au/goodfood/everything-you-wanted-to-know-about-dill-20220908-h268tf.html
5
Blue, N. (2023, January 30). What Is Savory: All About the Savory Herb and 4 Related Recipes. Recipes.net. Retrieved March 21, 2023, from https://recipes.net/articles/what-is-savory-herb-and-related-recipes/
6
Kale. (2021, October 19). The Nutrition Source. Retrieved March 21, 2023, from https://www.hsph.harvard.edu/nutritionsource/food-features/kale/
7
Chamomile – an overview. (n.d.). Science Direct. https://doi.org/10.1016/B978-0-323-85542-6.00003-2